1. Field of the Invention
This invention relates generally to electronic component testing apparatus. More particularly, this invention relates to spectrum analyzers within the electronic testing apparatus for characterizing electronic components to determine a frequency spectrum of a response characterization signal received from the electronic components. Even more particularly, this invention relates to spectrum analyzers to determine the frequency spectrum of a response characterization signal from magnetic head/media components.
2. Description of Related Art
The electronic component testers for evaluating magnetic head/media components require a spectrum analyzer to measure the performance related parameters of the magnetic head/media components such as the signal-to-noise ratio (SNR) and the Overwrite ability of the magnetic head/media components.
FIG. 1 is a simplified block diagram of a superheterodyne spectrum analyzer well known in the art and is described in “Agilent Spectrum Analysis Basics”, Application Note 150, January 2005, Agilent Technologies, Inc., Palo Alto, Calif., found www.Agilent.com, Jul. 24, 2006. An input signal f(t) 5 passes through an attenuator 10, then through a low-pass filter. The filtered input signal f(t) 5 is transferred through the mixer 20 where it is combined with a signal from the local oscillator (LO) 25 to form an intermediate frequency signal. Because the mixer 20 is a non-linear device, intermediate frequency signal includes not only the two original signals, but also their harmonics and the sums and differences (image signal) of the original frequencies and their harmonics.
The output of the mixer 20 is the input to the IF gain stage 30 where the mixed signal is amplified and passed to the intermediate frequency bandpass filter 40. The intermediate frequency (IF) bandpass filter 40 removes those harmonic and the sum and difference frequencies that are beyond the pass band of the bandpass filter 40. If any of the mixed signals fall within the pass band of the intermediate-frequency filter 40, it is further processed (amplified and perhaps compressed on a logarithmic scale). The output of the intermediate frequency filter 40 is transferred to the logarithmic amplifier 45 where it is logarithmically amplified. The logarithmically amplified signal is then transferred to the envelope detector 50 where it is essentially rectified. The video filter 55 filters the detected envelope signal and it is further processed for presentation on the display 60.
A ramp generator 65 creates the horizontal movement across the display 60 from left to right. The ramp signal of the ramp generator 65 also tunes the local oscillator 25 so that its frequency change is in proportion to the ramp voltage. The reference oscillator 70 provides a stable system reference timing signal for the local oscillator 25.
Since the output of a spectrum analyzer is an X-Y trace on the display 60, the trace on the display 60 presents the amplitude of the input signal f(t) 5 versus the frequency content of the input signal f(t) 5. The controls of the display 60 allow adjustment of the frequency span and the amplitude presentation for extraction of more information with regards to the frequency content and the amplitude of the component frequencies of the input signal f(t) 5.
An alternate to the superheterodyne spectrum analyzer of FIG. 1, as shown in FIG. 2, is a multi-channel spectrum analyzer as shown in Introduction to Communication Systems, Stremler, Addison-Wesley Publishing Co., Boston, Mass., 1977, p.: 146. The input signal f(t) 105 is applied to a bank of multiple bandpass filters 110a, 110b, . . . , 110n. Each filter of the bank of multiple bandpass filters 110a, 110b, . . . , 110n is constructed to cover a signal non-overlapping region of the frequency spectrum of the spectrum analyzer, such that the input signal f(t) 105 is decomposed into independent frequency bands of the frequency spectrum. The output of each of the bank of multiple bandpass filters 110a, 110b, . . . , 110n is the input to one of the energy determining circuits 115a, 115b, . . . , 115n. It is known in the art that as long as some voltage value of a input signal f(t) 105 is known (for example, peak or average) and the resistance across which this value is measured, the energy in the decomposed input signal f(t) 105 can be determined.
The threshold detector 130 determines the presence of the input signal f(t) 105 and activates a clocking circuit 135. The clocking circuit activates a selector switch 120 that transfers the energy signal output of each of the energy determining circuits 115a, 115b, . . . , 115n to the display 125. The clocking circuit 135 also provides the synchronizing timing signal for the display to present the frequency spectrum of the input signal f(t) 105.
“A Spectrum Analyzer Using a High Speed Hopping PLL Synthesizer” Kumagai, et al., Conference Proceedings Instrumentation and Measurement Technology Conference, May 1994, pp.: 523-525, Vol. 2, describes a spectrum analyzer for an RF LSI Tester. The spectrum analyzer uses a high speed hopping synthesizer in the down-conversion unit.
“A Simple Technique for Analog Tuning of Frequency Synthesizers”, Hauser, IEEE Transactions on Instrumentation and Measurement, December 1989, Vol.: 38, Issue: 6, pp.: 1141-1144 presents an analog implementation of the fractional N-phase-locked-loop variable-frequency synthesis technique. The Frequency Synthesizer implementation allows tuning over broad frequency ranges and provides a compact, low-power, local oscillator for a swept heterodyne, low-frequency, battery-operation.
U.S. Pat. No. 6,316,928 (Miyauchi) provides a spectrum analyzer that incorporates a YTO (YIG tuned oscillator) as a sweep frequency local oscillator and a YTF (YIG tuned filter) as a frequency pre-selector for an incoming signal and improves a C/N (carrier to noise) ratio.
U.S. Pat. No. 6,166,533 (Musha) describes a frequency spectrum analyzer having an improved carrier to noise ration for analyzing frequency spectrum of an input signal. The spectrum analyzer includes a frequency converters formed of a frequency mixer, a IF (intermediate frequency) filter and a local signal oscillator. The frequency mixer may employ a phase lock loop.
U.S. Pat. No. 5,847,559 (Takaoku, et al.) provides a local oscillator to be used in a spectrum analyzer that reduces dynamic spurious caused by a digital step sweep of the local oscillator. The local oscillator employs a phase lock loop.
U.S. Pat. No. 5,818,215 (Miyamae, et al.) teaches a spectrum analyzer that converts frequencies of an input signal using a local signal from a local signal generator. The spectrum analyzer then detects the frequency converted outputs, and sweeps the frequencies of the local signal generated by the local signal generator. The local signal generator includes a digital direct synthesizer, a variable frequency oscillator, and a phase locked loop for controlling the oscillation frequency of the variable frequency oscillator using the output of the digital direct synthesizer as a reference signal.
U.S. Pat. No. 5,038,096 (Obie, et al.) illustrates a spectrum analyzer for measuring the frequency spectrum of a pulsed input signal. The spectrum analyzer includes a synthesized local oscillator that includes a phase lock loop. The oscillator signal is mixed with the pulsed input signal and filtered to determine the peak voltage of a predetermined frequency component of the mixed input signal.
U.S. Pat. No. 4,430,611 (Boland) describes a frequency-spectrum analyzer with phase-lock loop for analyzing the frequency and amplitude of an input signal. The spectrum analyzer includes a voltage controlled oscillator (VCO) which is driven by a ramp generator, and a phase error detector circuit. The phase error detector circuit measures the difference in phase between the VCO and the input signal, and drives the VCO locking it in phase momentarily with the input signal. The input signal and the output of the VCO are fed into a correlator which transfers the input signal to a frequency domain, while providing an accurate absolute amplitude measurement of each frequency component of the input signal.